Bài giảng Hệ điều hành nâng cao - Chapter 19: Real - Time Systems

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Bài giảng Hệ điều hành nâng cao - Chapter 19: Real - Time Systems

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Bài giảng Hệ điều hành nâng cao - Chapter 19: Real - Time Systems trình bày về đặc điểm hệ thống, các chức năng của hệ thống, thời gian thực của hệ điều hành, lập kế hoạch CPU,...Mời bạn đọc cùng tham khảo bài giảng đề tìm hiểu rõ hơn về Hệ điều hành nâng cao.

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Chapter 19: Real-Time Systems Operating System Concepts – 8th Edition Operating System Concepts – 8th Edition 19.1 Silberschatz, Galvin and Gagne ©2009
Chapter 19: Real-Time Systems s System Characteristics s Features of Real-Time Systems s Implementing Real-Time Operating Systems s Real-Time CPU Scheduling s An Example: VxWorks 5.x Operating System Concepts – 8th Edition 19.2 Silberschatz, Galvin and Gagne ©2009
Objectives s To explain the timing requirements of real-time systems s To distinguish between hard and soft real-time systems s To discuss the defining characteristics of real-time systems s To describe scheduling algorithms for hard real-time systems Operating System Concepts – 8th Edition 19.3 Silberschatz, Galvin and Gagne ©2009
Overview of Real-Time Systems s A real-time system requires that results be produced within a specified deadline period. s An embedded system is a computing device that is part of a larger system (i.e., automobile, airliner). s A safety-critical system is a real-time system with catastrophic results in case of failure. s A hard real-time system guarantees that real-time tasks be completed within their required deadlines. s A soft real-time system provides priority of real-time tasks over non real-time tasks. Operating System Concepts – 8th Edition 19.4 Silberschatz, Galvin and Gagne ©2009
System Characteristics s Single purpose s Small size s Inexpensively mass-produced s Specific timing requirements Operating System Concepts – 8th Edition 19.5 Silberschatz, Galvin and Gagne ©2009
System-on-a-Chip s Many real-time systems are designed using system-on-a-chip (SOC) strategy s SOC allows the CPU, memory, memory-management unit, and attached peripheral ports (i.e., USB) to be contained in a single integrated circuit Operating System Concepts – 8th Edition 19.6 Silberschatz, Galvin and Gagne ©2009
Bus-Oriented System Operating System Concepts – 8th Edition 19.7 Silberschatz, Galvin and Gagne ©2009
Features of Real-Time Kernels s Most real-time systems do not provide the features found in a standard desktop system s Reasons include q Real-time systems are typically single-purpose q Real-time systems often do not require interfacing with a user q Features found in a desktop PC require more substantial hardware that what is typically available in a real-time system Operating System Concepts – 8th Edition 19.8 Silberschatz, Galvin and Gagne ©2009
Virtual Memory in Real-Time Systems s Address translation may occur via: 1. Real-addressing mode where programs generate actual addresses 2. Relocation register mode 3. Implementing full virtual memory Operating System Concepts – 8th Edition 19.9 Silberschatz, Galvin and Gagne ©2009
Address Translation Operating System Concepts – 8th Edition 19.10 Silberschatz, Galvin and Gagne ©2009
Implementing Real-Time Systems s In general, real-time operating systems must provide: 1. Preemptive, priority-based scheduling 2. Preemptive kernels 3. Latency must be minimized Operating System Concepts – 8th Edition 19.11 Silberschatz, Galvin and Gagne ©2009
Minimizing Latency s Event latency is the amount of time from when an event occurs to when it is serviced. Operating System Concepts – 8th Edition 19.12 Silberschatz, Galvin and Gagne ©2009
Interrupt Latency s Interrupt latency is the period of time from when an interrupt arrives at the CPU to when it is serviced Operating System Concepts – 8th Edition 19.13 Silberschatz, Galvin and Gagne ©2009
Dispatch Latency s Dispatch latency is the amount of time required for the scheduler to stop one process and start another Operating System Concepts – 8th Edition 19.14 Silberschatz, Galvin and Gagne ©2009
Real-Time CPU Scheduling s Periodic processes require the CPU at specified intervals (periods) s p is the duration of the period s d is the deadline by when the process must be serviced s t is the processing time Operating System Concepts – 8th Edition 19.15 Silberschatz, Galvin and Gagne ©2009
Scheduling of tasks when P2 has a higher priority than P1 Operating System Concepts – 8th Edition 19.16 Silberschatz, Galvin and Gagne ©2009
Rate Montonic Scheduling s A priority is assigned based on the inverse of its period s Shorter periods = higher priority; s Longer periods = lower priority s P1 is assigned a higher priority than P2. Operating System Concepts – 8th Edition 19.17 Silberschatz, Galvin and Gagne ©2009
Missed Deadlines with Rate Monotonic Scheduling Operating System Concepts – 8th Edition 19.18 Silberschatz, Galvin and Gagne ©2009
Earliest Deadline First Scheduling s Priorities are assigned according to deadlines: the earlier the deadline, the higher the priority; the later the deadline, the lower the priority Operating System Concepts – 8th Edition 19.19 Silberschatz, Galvin and Gagne ©2009
Proportional Share Scheduling s T shares are allocated among all processes in the system s An application receives N shares where N < T s This ensures each application will receive N / T of the total processor time Operating System Concepts – 8th Edition 19.20 Silberschatz, Galvin and Gagne ©2009